A 90-kg halfback running north with a speed of 10 m/s is tackled by a 120-kg opponent running south at 4 m/s.The collision is perfectly inelastic.Compute the velocity of the two players just after the tackle.
A)3 m/s south
B)2 m/s south
C)2 m/s north
D)3 m/s north

Question

Quizplus · Accepted Answer

In a perfectly inelastic collision, the two objects stick together after the collision and move with a common velocity. Let's assume that after the tackle, the combined mass of the two players is (90 + 120) kg = 210 kg.

Conservation of momentum:
Momentum before the collision = Momentum after the collision
(90 kg) x (10 m/s) + (120 kg) x (-4 m/s) = (210 kg) x v
(900 kg*m/s) - (480 kg*m/s) = (210 kg) x v
v = 2 m/s north

Therefore, the velocity of the two players just after the tackle is 2 m/s north. The correct answer is C) 2 m/s north.

A 90-Kg Halfback Running North with a Speed of 10